This lesson introduces the geological and geodynamic foundations of natural hydrogen systems, focusing on how mantle rocks, tectonic deformation, and fluid circulation interact to generate hydrogen through serpentinization. It explores the conceptual and numerical framework developed to understand why specific tectonic environments – particularly rifted basins and mountain belts – control the presence and productivity of hydrogen systems. The lesson emphasizes the role of temperature windows, mantle exhumation, and basin inversion processes as key parameters governing hydrogen generation potential.
1. Geological Concept of Natural Hydrogen Generation
Natural hydrogen in the subsurface is primarily linked to water–rock interaction processes, particularly serpentinization. This occurs when ultramafic mantle rocks such as olivine and pyroxene react with water, producing serpentine minerals and molecular hydrogen (H₂). In this system, hydrogen is not introduced externally but generated in situ within the lithosphere.
A key requirement is the exposure of mantle-derived rocks to circulating fluids. Under normal geological conditions, these rocks reside at depths of approximately 30–40 km within the mantle. Therefore, tectonic processes are required to bring them closer to the surface where water can interact with them.
The conceptual model presented in the course describes mountain ranges as dynamic systems where mantle rocks are exhumed and placed into an optimal thermal regime, allowing hydrogen generation to occur when water is available along deep fault networks.
2. Tectonic Mechanisms: Rifting and Mountain Building
Two major tectonic processes control mantle exhumation and hydrogen system development:
Rifting processes involve lithospheric stretching and basin formation. During this stage, the crust thins, and mantle material can rise closer to the surface. This is typical of oceanic basin formation, such as early Atlantic-type settings. However, while mantle exhumation occurs, the system often lacks optimal conditions for large-scale hydrogen accumulation.
In contrast, basin inversion and mountain building occur when previously stretched basins are compressed. This leads to the formation of mountain ranges where fragments of mantle are tectonically emplaced into shallower crustal levels. These orogenic systems are characterized by complex fault networks, enhanced fluid circulation pathways, and more favorable conditions for hydrogen generation.
The interplay between these two phases is part of the Wilson cycle, which describes the opening and closing of ocean basins over geological time.
3. Serpentinization Temperature Window and Fluid Requirements
A critical parameter identified in the simulations is temperature. Hydrogen generation through serpentinization is most efficient within a specific thermal range, approximately between 200°C and 350°C. Within this window, reaction kinetics between water and ultramafic rocks are optimized.
Below this range, reactions are too slow to produce significant hydrogen volumes. Above it, mineral stability changes and reaction pathways become less favorable.
Water availability is equally essential. The presence of large-scale fault systems enables deep fluid circulation, allowing water to penetrate mantle-derived rocks. Without active fluid pathways, hydrogen generation is severely limited, regardless of mantle presence or temperature suitability.
The intersection of three elements defines a “hydrogen sweet spot”:
mantle rock presence, appropriate temperature conditions, and active water circulation pathways.
4. Numerical Tectonic Simulations and Model Design
To investigate these processes, the course presents 2D numerical geodynamic models simulating rifting followed by basin inversion. These models incorporate crustal layering, mantle dynamics, surface processes such as erosion and sedimentation, and thermal evolution.
The simulations demonstrate how initial rifting creates basin structures and allows mantle upwelling. Over time, sediment deposition occurs, followed by tectonic compression that closes the basin and drives mountain formation. During this inversion phase, mantle fragments are transported upward into optimal temperature zones.
A key result of these simulations is the dynamic migration of mantle rocks into shallow crustal levels during mountain building phases, significantly increasing hydrogen generation potential.
5. Hydrogen Productivity: Rifting Versus Mountain Belts
Model results show a strong contrast between rift and mountain environments.
During early rifting, hydrogen generation remains limited due to insufficient mantle exposure and limited reactive volume. In contrast, during basin inversion and mountain building, hydrogen generation increases dramatically—up to approximately twenty times higher than in rift settings according to model outputs.
This difference is attributed to three factors. First, larger volumes of mantle are exhumed and remain trapped in the orogenic system. Second, temperature conditions stabilize within the optimal serpentinization range for longer durations. Third, sedimentary basins formed during orogeny provide improved reservoir and seal configurations for gas accumulation.
6. Sedimentary Systems and Reservoir Potential
Another critical element is sediment type. Rift basins are often dominated by fine-grained sediments, which are less effective for gas storage. In contrast, mountain belts develop more diverse sedimentary environments, including sandstones and carbonates, which provide better reservoir properties.
This distinction is essential for evaluating whether generated hydrogen can accumulate in extractable quantities. Without suitable reservoirs and seals, even high hydrogen generation rates may not translate into economically viable accumulations.
Tectonic simulations demonstrate that natural hydrogen systems are fundamentally controlled by lithospheric evolution. While rifting initiates mantle exhumation, it is the later stage of mountain building that provides optimal conditions for large-scale hydrogen generation and accumulation. The coupling of mantle exposure, thermal evolution, and sedimentary architecture defines the most prospective environments for exploration.